The present invention relates to a process for metering fuel with a fuel injector.
German Published Patent Application No.196 26 576 describes a process and a fuel injector that has a solenoid armature and a solenoid coil which form, together with the housing of the fuel injector, a magnetic flux circuit. When the coil is actuated, the armature is pulled into the coil, which lifts a valve closing body connected with the armature off of a valve seat face, and fuel is ejected out of the fuel injector. To improve the swirling of the ejected fuel, the valve closing body has swirl grooves formed in it that produce a swirling flow.
To meter fuel with the fuel injector disclosed by German Published Patent Application No.196 26 576, an excitation voltage is applied to the magnetic coil, whereby the metered quantity of fuel is varied from when the excitation voltage is turned on to when it is turned off.
The disadvantage of the prior-art fuel injector disclosed by German Published Patent Application No.196 26 576 is that the properties of the ejected fuel jet are determined by the design, so that only the metered quantity of fuel can be changed and not the distribution of the fuel in the combustion chamber into which the fuel is injected.
Another disadvantage is that a change in the jet field of ejected fuel requires a change in the manufacturing process of the fuel injector, so that differing customer requirements can only be met to a limited extent.
By contrast, the process according to the present invention for metering fuel with a fuel injector has the advantage that the properties and thus the pattern of the ejected fuel jet can be varied without changing the design of the fuel injector so that the fuel distribution of the fuel ejected by the fuel injector can be changed while operating the injector. Moreover, the fuel injector covers a greater range of application, which improves engine behavior.
It is advantageous for the valve stroke to have a low opening speed so that the transition from the preliminary flow (which is at least approximately free of swirl) to the swirling flow is essentially continuous, and the fuel ejected near the ejection end of the fuel injector has an at least approximately uniform distribution. The strong stroke throttling of the initial flow in which the valve has just opened with an early overlapping swirling flow gives the fuel a low speed; this distributes the fuel essentially near the ejection end of the fuel injector. This allows the fuel to accumulate, e.g., in the area of a spark plug, and to be uniformly distributed there so that the fuel advantageously ignites even if there is only a small quantity. Moreover, this process is especially suitable for small combustion chambers in which a strong jet penetration is undesired to prevent wetting an inside wall of a combustion chamber of the internal combustion engine or one of its pistons.
It is advantageous that: The valve stroke occurs with a high opening speed so that the approximately swirl-free preliminary flow produces a slender, tubular, preliminary jet; that the transition from the (at least approximately) swirl-free preliminary flow to the swirling flow is essentially abrupt; and that the swirling flow produces a conical, broad, main jet following the slender, tubular, preliminary jet. This distributes the injected fuel over a large volume, whereby the fuel jet produced by the preliminary flow has a high speed in the injection direction, and the fuel flow produced by the swirling flow has a high velocity component perpendicular to the injection direction.
It is advantageous that the opening speed is varied by changing the opening time of an essentially constant valve stroke. The xe2x80x9copening timexe2x80x9d is the time required to open the fuel injector. This makes it especially simple to use the process.
It is advantageous that the fuel is injected directly into a combustion chamber of an external-ignition internal combustion engine, and that the opening speed is affected by the mode of operation of the internal combustion engine. One can produce the jet pattern desired for the respective operating point to optimize the operational behavior of the internal combustion engine by specifically controlling the fuel injector while the internal combustion engine is operating.
It is also advantageous for the valve stroke to have a low opening speed when the internal combustion engine is in stratified-charge operation, and for the valve stroke to have a high opening speed when the internal combustion engine is in homogenous operation. When the internal combustion engine is in stratified-charge operation, the fuel collects mainly in the area of a spark plug for superior fuel ignition. When the internal combustion engine is in homogenous operation, the fuel is distributed throughout the combustion chamber to optimally mix the fuel with the available air sucked into the internal combustion engine for optimal combustion.